The hashing feature described in this section applies to traffic going over LAG and MC-LAG. LAG link mapping profile feature gives operators full control of which links SAPs/network interface use on a LAG egress and how the traffic is rehashed on a LAG link failure. Some benefits that such functionality provides include:
Ability to perform management level admission control onto LAG ports therefore increasing overall LAG BW utilization and controlling LAG behavior on a port failure.
Ability to strictly enforce QoS contract on egress for a SAP/network interface or a group of SAPs/network interfaces by forcing it/them to egress over a single port and using access adapt-qos link or port-fair mode.
To enable LAG Link Mapping Profile Feature on a LAG, operators configure one or more of the available LAG link mapping profiles on the LAG and then assign that profiles to all or a subset of SAPs and network interfaces as needed. Enabling per LAG link Mapping Profile is allowed on a LAG with services configured, a small outage may take place as result of re-hashing SAP/network interface when a lag profile is assigned to it.
Each LAG link mapping profile allows operators to configure:
primary link
Primary link defines a port of the LAG to be used by a SAP/network interface when the port is UP. Note that a port cannot be removed from a LAG if it is part of any LAG link profile.
secondary link
Secondary link defines a port of the LAG to be used by a SAP/network interface as a backup when the primary link is not available (not configured or down) and the secondary link is UP.
When neither primary, nor secondary links are available (not configured or down), use one of the following modes of operation:
discard
Traffic for a specific SAP/network interface is dropped to protect other SAPs/network interfaces from being impacted by re-hashing these SAPs/network interfaces over remaining active LAG ports.
per-link-hash
Traffic for a specific SAP/network interface is re-hashed over remaining active ports of a LAG links using per-link-hashing algorithm. This behavior ensures SAP/network interfaces using this profile are given available resources of other active LAG ports even if that means impacting other SAP/network interfaces on the LAG. The system uses the QoS configuration to provide fairness and priority if congestion is caused by the default-hash recovery.
LAG link mapping profiles, can be enabled on a LAG as long as the following conditions are met:
LAG port-type must be standard.
LAG access adapt-qos must be link or port-fair (for LAGs in mode access or hybrid)
All ports of a LAG on a router must belong to a single sub-group.
Access adapt-qos mode is distribute include-egr-hash-cfg.
LAG link mapping profile can coexist with any-other hashing used over a specific LAG (for example, per flow hashing or per-link-hashing). SAPs/network interfaces that have no link mapping profile configured are subject to LAG hashing, while SAPs/network interfaces that have configured LAG profile assigned are subject to LAG link mapping behavior, which is described above.